Objective optical element, optical pickup apparatus and optical disc driving apparatus

Abstract

An objective optical element for use in an optical pickup apparatus for recording and/or reproducing information on first—third optical information recording media using first—third light fluxes respectively, includes: a first phase structure for compensating a deterioration in a performance forming the converged spot on the information recording surface of the first optical information recording medium caused by an temperature change, a second phase structure for reducing a spherical aberration based on a thickness difference between the protective substrates of the first and second optical information media or the a wavelength difference between the first and second wavelengths, and a third phase structure for reducing a spherical aberration based on a thickness difference between the protective substrate of the first and third optical information media.

1. An objective optical element for use in an optical pickup apparatus for recording and/or reproducing information on a first optical information recording medium having a protective substrate with a thickness t 1  using a first light flux with a wavelength λ 1  emitted by a first light source,
 for recording and/or reproducing information on a second optical information recording medium having a protective substrate with a thickness t 2  (t 1 ≦t 2 ) using a second light flux with a wavelength λ 2  (λ 1 <λ 2 ) emitted by a second light source and 
 for recording and/or reproducing information on a third optical information recording medium having a protective substrate with a thickness t 3  (t 2 <t 3 ) using the third light flux (λ 2 <λ 3 ) emitted by the third light source and 
 for forming a converged spot on an information recording surface of each of the first through third optical information recording media, the objective optical element comprising: 
 a first phase structure for compensating a deterioration in a performance forming the converged spot on the information recording surface of the first optical information recording medium caused by an temperature change; 
 a second phase structure for reducing a spherical aberration based on a thickness difference between the protective substrate t 1  and the protective substrate t 2  or a wavelength difference between the wavelength λ 1  and the wavelength λ 2 ; and 
 a third phase structure for reducing a spherical aberration based on a thickness difference between the protective substrate t 1  and the protective substrate t 3 . 
 
   
   
     2. The objective optical element of  claim 1 ,
 wherein the first phase structure has a cross section including an optical axis whose shape is: 
 a phase difference providing structure providing a longer optical path length on a farther position from the optical axis when the position is in a range from the optical axis to a predefined height on the phase difference providing structure and providing a shorter optical path length on a farther position from the optical axis when the position is higher than the predefined height from the optical axis on the phase difference providing structure; or 
 a phase difference providing structure providing a shorter optical path length on a farther position from the optical axis when the position is in a range from the optical axis to a predefined height on the cross section on the phase difference providing structure and providing a longer optical path length on a farther position from the optical axis when the position is higher from the predefined height from the optical axis on the phase difference providing structure. 
 
   
   
     3. The objective optical element of  claim 2 ,
 wherein an area in the first phase structure providing a same phase to a phase at the predefined height of the first phase structure includes a position which is at 70% of an effective light flux diameter of the first light flux. 
 
   
   
     4. The objective optical element of  claim 1 ,
 wherein the first phase structure is a phase difference providing structure which generates α 1 -th order diffracted light flux having a maximum diffraction efficiency among diffracted light fluxes generated when the first light flux enters into the first phase structure, 
 generates β 1 -th (β 1 <α 1 ) order diffracted light flux having a maximum diffraction efficiency among diffracted light fluxes generated when the second light flux enters into the first phase structure, and 
 generates γ 1 -th (γ 1 ≦β 1 ) order diffracted light flux having a maximum diffraction efficiency among diffracted light fluxes generated when the third light flux enters into the first phase structure. 
 
   
   
     5. The objective optical element of  claim 2 ,
 wherein a cross section including an optical axis of the phase difference providing structure has a stepped structure. 
 
   
   
     6. The objective optical element of  claim 5 ,
 wherein the first phase structure satisfies following expressions:
     p=INT ( d ( n 1−1)/λ1), 
     q=INT ( d ( n 3−1)/λ3) and 
     p>q,    
 
 where d is a step amount of the first phase structure, 
 n 1  is a refractive index of a medium of the first phase structure for the first light flux, 
 n 3  is a refractive index of a medium of the first phase structure for the third light flux, and 
 Int(X) is an integer value closest to X. 
 
   
   
     7. The objective optical element of  claim 1 ,
 wherein the second phase structure diffracts the second light flux and does not diffract the first light flux and the third light flux. 
 
   
   
     8. The objective optical element of  claim 7 ,
 wherein the second phase structure is a structure including a plurality of patterns arranged concentrically, 
 each of the plurality of patterns has a cross section including an optical axis in a stepped shape with a plurality of levels, and 
 each step of the stepped shape is shifted by height of steps corresponding to a predefined number A of the plurality of levels for every predefined number A of the levels. 
 
   
   
     9. The objective optical element of  claim 8 ,
 wherein the predefined number A of the levels is one of 4, 5 and 6. 
 
   
   
     10. The objective optical element of  claim 8 ,
 wherein an amount of an optical path difference generated by one of the steps is twice of the first wavelength λ 1 . 
 
   
   
     11. The objective optical element of  claim 7 ,
 wherein the second phase structure satisfies 40<νd2<70, 
 where νd2 is an Abbe number of a medium of the second phase structure. 
 
   
   
     12. The objective optical element of  claim 1 ,
 wherein the second phase structure is a diffractive structure which generates α 2 -th order diffracted light flux having a maximum diffraction efficiency among diffracted light fluxes generated when the first light flux enters into the second phase structure, 
 generates β 2 -th (β 2 <α 2 ) order diffracted light flux having a maximum diffraction efficiency among diffracted light fluxes generated when the second light flux enters into the second phase structure, and 
 generates γ 2 -th (γ 2 <β 2 ) order diffracted light flux having a maximum diffraction efficiency among diffracted light fluxes generated when the third light flux enters into the second phase structure. 
 
   
   
     13. The objective optical element of  claim 1 ,
 wherein the third phase structure is a diffractive structure which diffracts the third light flux and does not diffract the first light flux and the second light flux. 
 
   
   
     14. The objective optical element of  claim 13 ,
 wherein the third phase structure is a structure including a plurality of patterns arranged concentrically, 
 each of the plurality of patterns has a cross section including an optical axis in a stepped shape with a plurality of levels, 
 each step of the stepped shape is shifted by height of steps corresponding to a predefined number B of the plurality of levels for every predefined number B of the levels. 
 
   
   
     15. The objective optical element of  claim 14 ,
 wherein the third phase structure satisfies 40<νd3<70, 
 where νd3 is an Abbe number of a medium of the third phase structure and 
 the predefined number B of the levels is 2. 
 
   
   
     16. The objective optical element of  claim 15 ,
 wherein an amount of an optical path difference generated by one of the steps is five times of the first wavelength λ 1 . 
 
   
   
     17. The objective optical element of  claim 14 ,
 wherein the third phase structure satisfies 24<νd3<40, 
 where νd3 is an Abbe number of a medium of the third phase structure and 
 the predefined number B of the levels is 3. 
 
   
   
     18. The objective optical element of  claim 17 ,
 wherein an amount of an optical path difference generated by one of the steps is five times or seven times of the first wavelength λ 1 . 
 
   
   
     19. The objective optical element of  claim 14 ,
 wherein the third phase structure satisfies 20<νd3<26, 
 where νd3 is an Abbe number of a medium of the third phase structure and 
 the predefined number B of levels is 4. 
 
   
   
     20. The objective optical element of  claim 19 ,
 wherein an amount of an optical path difference generated by one of the steps is seven times of the first wavelength λ 1 . 
 
   
   
     21. The objective optical element of  claim 1 ,
 wherein the third phase structure is a diffractive structure which generates α 3 -th order diffracted light flux having a maximum diffraction efficiency among diffracted light fluxes generated when the first light flux enters into the third phase structure, 
 generates β 3 -th (β 3 <α 3 ) order diffracted light flux having a maximum diffraction efficiency among diffracted light fluxes generated when the second light flux enters into the third phase structure, and 
 generates β 3 -th (β 3 <α 3 ) order diffracted light flux having a maximum diffraction efficiency among diffracted light fluxes generated when the third light flux enters into the third phase structure. 
 
   
   
     22. The objective optical element of  claim 21 ,
 wherein the third phase structure satisfies 20<νd3<40, 
 where νd3 is an Abbe number of a medium of the third phase structure. 
 
   
   
     23. The objective optical element of  claim 22 ,
 wherein α 3  is an odd number. 
 
   
   
     24. The objective optical element of  claim 1 ,
 wherein the objective optical element comprises a light converging optical element and an aberration correcting lens group. 
 
   
   
     25. The objective optical element of  claim 24 , consisting of two elements formed in two groups and including at least one light converging optical element. 
   
   
     26. The objective optical element of  claim 24 , consisting of three elements formed in two groups and including at least a light converging optical element formed in one group and,
 wherein one of the two groups includes two optical elements which are made of different media each other and are attached each other. 
 
   
   
     27. The objective optical element of  claim 24 , consisting of three elements formed in three groups and including at least one light converging optical element. 
   
   
     28. The objective optical element of  claim 24 ,
 wherein the light converging optical element is formed of a resin material. 
 
   
   
     29. The objective optical element of  claim 24 ,
 wherein each element forming the objective optical element is formed of a resin material. 
 
   
   
     30. An optical pickup apparatus, comprising:
 a first light source for emitting a first light flux with a wavelength λ 1  for recording and/or reproducing information on a first optical information recording medium having a protective substrate with a thickness t 1 ; 
 a second light source for emitting a second light flux with a wavelength λ 2  (λ 1 <λ 2 ) for recording and/or reproducing information on a second optical information recording medium having a protective substrate with a thickness t 2  (t 1 ≦t 2 ); 
 a third light source for emitting a third light flux (λ 2 <λ 3 ) for recording and/or reproducing information on a third optical information recording medium having a protective substrate with a thickness t 3  (t 2 <t 3 ); and 
 the objective optical element of  claim 1 . 
 
   
   
     31. An optical disc drive apparatus, comprising:
 the optical pickup apparatus of  claim 30 ; and 
 a moving unit for moving the optical pickup apparatus in a radius direction of each of the first to third optical information recording media.